JP7580596B2 - Electrolyte for lithium-sulfur battery and lithium-sulfur battery including the same - Google Patents

Description

This application claims the benefit of priority to Korean Patent Application No. 10-2021-0071883 dated June 3, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

The present invention relates to an electrolyte for lithium-sulfur batteries and a lithium-sulfur battery containing the same.

As the range of secondary battery applications expands from small portable electronic devices to medium and large electric vehicles (EVs), energy storage systems (ESSs), electric ships, etc., the demand for lithium secondary batteries with high capacity, high energy density and long life is rapidly increasing.

Lithium metal has a theoretically very high specific capacity of 3,860 mAh/g, and because it has a low potential and very low density as an anode material, various attempts have been made to use it as a battery anode.

In particular, a lithium-sulfur secondary battery refers to a battery system that uses a sulfur-based material having a "S-S bond (Sulfur-Sulfur Bond)" as the positive electrode active material and lithium metal as the negative electrode active material. Sulfur, the main material of the positive electrode active material, has low weight per atom and is abundant in resources, making it easy to supply and demand. It is also inexpensive, which can reduce battery manufacturing costs, and is non-toxic and environmentally friendly.

In particular, the lithium-sulfur secondary battery has a theoretical discharge capacity of 1,675 mAh/g-sulfur and can theoretically realize a high energy storage density of 2,600 Wh/kg by weight. This is much higher than the theoretical energy density of other battery systems currently being researched (Ni-MH battery: 450 Wh/kg, Li-FeS battery: 480 Wh/kg, Li- _MnO2 battery: 1,000 Wh/kg, Na-S battery: 800 Wh/kg) and lithium ion batteries (250 Wh/kg), and is therefore attracting much attention in the market for medium and large secondary batteries that are currently being developed.

One of the factors that affect the lifespan of the lithium-sulfur secondary battery is the degradation of the lithium negative electrode, which can occur due to reactions with the positive electrode active material and with the electrolyte. The degradation of the negative electrode can result in the formation of dendrites, which has been pointed out as a problem in that it reduces the Coulombic Efficiency (C.E.). In particular, if the dendrites are formed in a one-dimensional form, an internal short circuit can occur through the separator containing pores, which can cause safety issues and shorten the battery's lifespan due to the combustion of the electrolyte.

Therefore, in order to improve the problems of lithium-sulfur batteries caused by the dendrite phenomenon, research is needed to suppress the formation of dendrites by uniformly plating and stripping lithium from the surface of the negative electrode.

Korean Patent Publication No. 10-2019-0119963

To solve the above problems, the inventors aim to provide a lithium-sulfur battery with improved battery life and efficiency by adding a dioxolane derivative to the electrolyte for the lithium-sulfur battery.

According to a first aspect of the present invention,
The present invention provides an electrolyte for a lithium-sulfur battery, comprising a lithium salt, an organic solvent, and an additive, the additive comprising a compound represented by the following Chemical Formula 1:

[Chemical Formula 1]

In the above formula 1, R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen; deuterium; a substituted or unsubstituted C1 to C60 alkyl group; a substituted or unsubstituted C6 to C60 aryl group; a substituted or unsubstituted C1 to C60 alkoxy group; and a substituted or unsubstituted C6 to C60 aryloxy group, and at least one of R1 to R6 is not H.

In one embodiment of the present invention, R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen; deuterium; a substituted or unsubstituted C1 to C20 alkyl group; a substituted or unsubstituted C6 to C20 aryl group; a substituted or unsubstituted C1 to C20 alkoxy group; and a substituted or unsubstituted C6 to C20 aryloxy group, and at least one of R1 to R6 may not be H.

In one embodiment of the present invention, R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen; deuterium; and substituted or unsubstituted C1 to C10 alkyl groups, and at least one of R1 to R6 may not be H.

In one embodiment of the present invention, R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, methyl, ethyl, propyl, n-propyl, isopropyl, butyl, n-butyl, isobutyl, tert-butyl, sec-butyl, 1-methyl-butyl, 1-ethyl-butyl, pentyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 4-methyl-2-pentyl, 3,3-dimethylbutyl, and 2-ethylbutyl, and at least one of R1 to R6 may not be H.

In one embodiment of the present invention, the compound represented by Chemical Formula 1 is selected from the group consisting of 2-methyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 2-ethyl-2-methyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2,2,4-trimethyl-1,3-dioxolane, and combinations thereof.

In one embodiment of the present invention, the electrolyte for the lithium-sulfur battery may contain the compound represented by Chemical Formula 1 in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

In one embodiment of the present invention, the compound represented by Chemical Formula 1 is 2-methyl-1,3-dioxolane, and the lithium-sulfur battery electrolyte may contain 0.1 to 5 wt % of the compound represented by Chemical Formula 1 based on the total weight of the electrolyte.

According to a second aspect of the present invention,
The present invention provides a lithium-sulfur battery comprising: a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and the electrolyte.

The lithium-sulfur battery according to the present invention contains a dioxolane derivative as an additive in the electrolyte, and forms a protective film on the surface of the negative electrode, which is a lithium-based metal, through ring-opening polymerization, suppressing the formation of lithium dendrites and improving the battery life and coulombic efficiency.

All of the specific examples provided by the present invention can be achieved by the following description. The following description should be understood as describing preferred specific examples of the present invention, and it should be understood that the present invention is not necessarily limited thereto.

The term "polysulfide" used in this specification is a concept which includes both "polysulfide ions (S _x ^2- , x=8, 6, 4, 2)" and "lithium polysulfides (Li ₂ S _x or LiS _x ^- , x=8, 6, 4, 2)."

As used herein, the term "substituted" means that a hydrogen atom bonded to a carbon atom of a compound is replaced with another substituent, and the position of the substitution is not limited to the position at which a hydrogen atom is replaced, i.e., a position at which a substituent can be substituted, and when two or more substitutions are made, the two or more substituents may be the same or different.

As used herein, the optional substituents of "substituted or unsubstituted" may be one or more substituents selected from the group consisting of deuterium; halogen; cyano group; alkyl group having 1 to 60 carbon atoms; alkenyl group having 2 to 60 carbon atoms; alkynyl group having 2 to 60 carbon atoms; cycloalkyl group having 3 to 60 carbon atoms; heterocycloalkyl group having 2 to 60 carbon atoms; aryl group having 5 to 60 carbon atoms; heteroaryl group having 2 to 60 carbon atoms; alkoxy group having 1 to 60 carbon atoms; aryloxy group having 5 to 60 carbon atoms; alkylsilyl group having 1 to 60 carbon atoms; and arylsilyl group having 6 to 60 carbon atoms. When there are multiple substituents, they may be the same or different.

Electrolyte for Lithium-Sulfur Battery According to the present invention, there is provided an electrolyte for a lithium-sulfur battery, comprising a lithium salt, an organic solvent, and an additive, wherein the additive comprises a compound represented by the following Chemical Formula 1:

[Chemical Formula 1]

In the above Chemical Formula 1,
R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen; deuterium; a substituted or unsubstituted C1 to C60 alkyl group; a substituted or unsubstituted C6 to C60 aryl group; a substituted or unsubstituted C1 to C60 alkoxy group; and a substituted or unsubstituted C6 to C60 aryloxy group, wherein at least one of R1 to R6 is not H.

The lithium-sulfur battery electrolyte contains dioxolane derivatives, which are compounds represented by Chemical Formula 1, as an additive, and thus a negative electrode protective film is formed on the surface of the lithium-based metal used as the negative electrode through ring opening polymerization, reducing the formation of dendrites and improving the life and efficiency characteristics of the battery through efficient plating and stripping processes.

R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen; deuterium; a substituted or unsubstituted C1 to C60 alkyl group; a substituted or unsubstituted C6 to C60 aryl group; a substituted or unsubstituted C1 to C60 alkoxy group; and a substituted or unsubstituted C6 to C60 aryloxy group, and at least one of R1 to R6 may not be H.

R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen; deuterium; a substituted or unsubstituted C1 to C40 alkyl group; a substituted or unsubstituted C6 to C40 aryl group; a substituted or unsubstituted C1 to C40 alkoxy group; and a substituted or unsubstituted C6 to C40 aryloxy group, and at least one of R1 to R6 may not be H.

R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen; deuterium; a substituted or unsubstituted C1 to C20 alkyl group; a substituted or unsubstituted C6 to C20 aryl group; a substituted or unsubstituted C1 to C20 alkoxy group; and a substituted or unsubstituted C6 to C20 aryloxy group, and at least one of R1 to R6 may not be H.

R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen; deuterium; a substituted or unsubstituted C1 to C10 alkyl group; a substituted or unsubstituted C6 to C10 aryl group; a substituted or unsubstituted C1 to C10 alkoxy group; and a substituted or unsubstituted C6 to C10 aryloxy group, and at least one of R1 to R6 may not be H.

R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen; deuterium; a substituted or unsubstituted C1 to C10 alkyl group; a substituted or unsubstituted C6 to C10 aryl group; and a substituted or unsubstituted C1 to C10 alkoxy group; and at least one of R1 to R6 may not be H.

R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen; deuterium; a substituted or unsubstituted C1 to C10 alkyl group; a substituted or unsubstituted C6 to C10 aryl group; and a substituted or unsubstituted C6 to C10 aryloxy group, and at least one of R1 to R6 may not be H.

R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen; deuterium; substituted or unsubstituted C1 to C10 alkyl groups; substituted or unsubstituted C1 to C10 alkoxy groups; and substituted or unsubstituted C6 to C10 aryloxy groups, and at least one of R1 to R6 may not be H.

R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen; deuterium; a substituted or unsubstituted C6 to C10 aryl group; a substituted or unsubstituted C1 to C10 alkoxy group; and a substituted or unsubstituted C6 to C10 aryloxy group, and at least one of R1 to R6 may not be H.

R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen; deuterium; substituted or unsubstituted C1 to C10 alkyl groups; and substituted or unsubstituted C6 to C10 aryl groups; and at least one of R1 to R6 may not be H.

R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen; deuterium; and substituted or unsubstituted C1 to C10 alkyl groups; and at least one of R1 to R6 may not be H.

R1 to R6 are the same or different and each independently represent hydrogen; deuterium; methyl; ethyl; propyl; n-propyl; isopropyl; butyl; n-butyl; isobutyl; tert-butyl; sec-butyl; 1-methyl-butyl; 1-ethyl-butyl; pentyl; n-pentyl; isopentyl; neopentyl; tert-pentyl; hexyl; n-hexyl; 1-methylpentyl; 2-methylpentyl; 4-methyl-2-pentyl; 3,3-dimethylbutyl; 2-ethyl butyl group; heptyl group; n-heptyl group; 1-methylhexyl group; cyclopentylmethyl group; cyclohexylmethyl group; octyl group; n-octyl group; tert-octyl group; 1-methylheptyl group; 2-ethylhexyl group; 2-propylpentyl group; n-nonyl group; 2,2-dimethylheptyl group; 1-ethyl-propyl group; 1,1-dimethyl-propyl group; isohexyl group; 2-methylpentyl group; 4-methylhexyl group; and 5-methylhexyl group; and at least one of R1 to R6 may not be H.

R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, methyl, ethyl, propyl, n-propyl, isopropyl, butyl, n-butyl, isobutyl, tert-butyl, sec-butyl, 1-methyl-butyl, 1-ethyl-butyl, pentyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 4-methyl-2-pentyl, 3,3-dimethylbutyl, and 2-ethylbutyl, and at least one of R1 to R6 may not be H.

R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a methyl group, an ethyl group, a propyl group, an n-propyl group, an isopropyl group, a butyl group, an n-butyl group, an isobutyl group, a tert-butyl group, and a sec-butyl group, and at least one of R1 to R6 may not be H.

In this specification, the alkyl group specifically includes a methyl group, an ethyl group, a propyl group, an n-propyl group, an isopropyl group, a butyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a sec-butyl group, a 1-methyl-butyl group, a 1-ethyl-butyl group, a pentyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a hexyl group, an n-hexyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 4-methyl-2-pentyl group, a 3,3-dimethylbutyl group, a 2-ethylbutyl group, a heptyl group, and an n-heptyl group. can be selected from the group consisting of, but is not limited to, 1-methylhexyl group, cyclopentylmethyl group, cyclohexylmethyl group, octyl group, n-octyl group, tert-octyl group, 1-methylheptyl group, 2-ethylhexyl group, 2-propylpentyl group, n-nonyl group, 2,2-dimethylheptyl group, 1-ethyl-propyl group, 1,1-dimethyl-propyl group, isohexyl group, 2-methylpentyl group, 4-methylhexyl group, and 5-methylhexyl group.

In this specification, the aryl group can be specifically selected from the group consisting of a phenyl group, a biphenyl group, a terphenyl group, a quaterphenyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, a pyrenyl group, a perylenyl group, a triphenyl group, a krysenyl group, a fluorenyl group, and a triphenylenyl group, but is not limited thereto.

In this specification, the alkoxy group can be specifically selected from the group consisting of methoxy, ethoxy, n-propoxy, i-propyloxy, n-butoxy, isobutoxy, tert-butoxy, sec-butoxy, n-pentyloxy, neopentyloxy, isopentyloxy, n-hexyloxy, 3,3-dimethylbutyloxy, 2-ethylbutyloxy, n-octyloxy, n-nonyloxy, and n-decyloxy, but is not limited thereto.

In this specification, the aryloxy group can be specifically selected from the group consisting of a phenoxy group, a p-tolyloxy group, a m-tolyloxy group, a 3,5-dimethyl-phenoxy group, a 2,4,6-trimethylphenoxy group, a p-tert-butylphenoxy group, a 3-biphenyloxy group, a 4-biphenyloxy group, a 1-naphthyloxy group, a 2-naphthyloxy group, a 4-methyl-1-naphthyloxy group, a 5-methyl-2-naphthyloxy group, a 1-anthryloxy group, a 2-anthryloxy group, a 9-anthryloxy group, a 1-phenanthryloxy group, a 3-phenanthryloxy group, and a 9-phenanthryloxy group, but is not limited thereto.

The compounds represented by the above chemical formula 1 are 2-methyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 2-ethyl-2-methyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2,2,4-trimethyl ... -trimethyl-1,3-dioxolane) and combinations thereof, and preferably 2-methyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 2-ethyl-2-methyl-1,3-dioxolane, and combinations thereof.

The lithium-sulfur battery electrolyte may contain 0.1 wt% or more, 0.3 wt% or more, 0.5 wt% or more, 0.7 wt% or more, 0.9 wt% or more of the compound represented by Chemical Formula 1, and 5 wt% or less, 4.6 wt% or less, 4.2 wt% or less, 3.8 wt% or less, 3.4 wt% or less, 3 wt% or less of the compound represented by Chemical Formula 1, based on the total weight of the electrolyte. If the lithium-sulfur battery electrolyte contains less than 0.1 wt% of the compound represented by Chemical Formula 1 based on the total weight of the electrolyte, the amount of the compound added is small, the formation of the anode protective film is faint, and the intended function of the dioxolane derivative additive may not be achieved. If the lithium-sulfur battery electrolyte contains more than 5 wt% of the compound represented by Chemical Formula 1 based on the total weight of the electrolyte, an overvoltage may be induced in the battery, causing problems in the operation of the battery.

The compound represented by Chemical Formula 1 in the lithium-sulfur battery electrolyte is 2-methyl-1,3-dioxolane, and the lithium-sulfur battery electrolyte may contain 0.1 to 5 wt % of the compound represented by Chemical Formula 1 based on the total weight of the electrolyte.

The organic solvent may include a compound selected from the group consisting of linear ether compounds, cyclic ether compounds, and combinations thereof.

The linear ether compound may include those selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, diisobutyl ether, ethyl methyl ether, ethyl propyl ether, ethyl tert-butyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, dimethoxypropane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, dipropylene glycol dimethylene ether, butylene glycol ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, diethylene glycol tert-butyl ethyl ether, ethylene glycol ethyl methyl ether, and combinations thereof.

The cyclic ether compounds are 1,3-dioxolane, 4,5-dimethyl-dioxolane, 4,5-diethyl-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 2,5-dimethoxytetrahydrofuran, 2-ethoxytetrahydrofuran, 2-methyl-1,3-dioxolane, 2-vinyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2-methoxy-1,3-dioxolane, 2-ethyl-2-methyl-1,3-dioxolane, tetrahydropyran, 1,4-dioxane, 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, isosorbide dimethyl ether (isosorbide dimethyl ether) and combinations thereof.

The electrolyte for a lithium-sulfur battery of the present invention may contain a lithium salt, which is a material that is easily dissolved in an organic solvent, such as LiCl, LiBr, LiI, _LiClO4 , _LiBF4 , _LiB10Cl10 , LiB(Ph) ₄ , _LiC4BO8 , _LiPF6 , LiCF3SO3 _{, LiCF3CO2} , LiAsF6, _{LiSbF6 , LiAlCl4} , _LiSO3CH3 , _LiSO3CF3 , _{LiSCN ,} LiC _{(CF3SO2 )3, LiN(CF3SO2 ) 2 , LiN ( C2F5SO2} ) ₂ , LiN _{( SO2F ) 2} , and LiN( _SO2F ) _{2 .} The lithium borane may be selected from the group consisting of lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate and lithium imide, and is preferably LiN(CF ₃ SO ₂ ) ₂ (LITFSI).

The concentration of the lithium salt is 0.1 to 5.0 M, preferably 0.2 to 3.0 M, and more preferably 0.5 to 2.5 M, depending on several factors such as the exact composition of the mixture contained in the electrolyte, the solubility of the salt, the conductivity of the dissolved salt, the charging and discharging conditions of the battery, the operating temperature, and other factors known in the lithium battery field. If less than 0.1 M is used, the conductivity of the electrolyte may decrease, resulting in a decrease in the performance of the electrolyte, and if more than 5.0 M is used, the viscosity of the electrolyte may increase, resulting in a decrease in the mobility of the lithium ions (Li ⁺ ).

The electrolyte for lithium-sulfur batteries of the present invention may further include additives commonly used in the relevant technical field in addition to the above-mentioned composition, such as lithium nitrate (LiNO ₃ ), potassium nitrate (KNO ₃ ), cesium nitrate (CsNO ₃ ), magnesium nitrate (Mg(NO ₃ ) ₂ ), barium nitrate (Ba(NO ₃ ) ₂ ), lithium nitrite (LiNO ₂ ), potassium nitrite (KNO ₂ ), cesium nitrite (CsNO ₂ ), and combinations thereof.

The method for producing the electrolyte for lithium-sulfur batteries according to the present invention is not particularly limited in the present invention, and it can be produced by a conventional method known in the industry.

Lithium-Sulfur Battery The lithium-sulfur battery according to the present invention comprises a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, the electrolyte comprising the lithium-sulfur battery electrolyte according to the present invention.

The positive electrode may include a positive electrode current collector and a positive electrode active material layer applied to one or both sides of the positive electrode current collector.

The positive electrode current collector is not particularly limited as long as it supports the positive electrode active material, does not induce chemical changes in the battery, and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, baked carbon, copper or stainless steel surface-treated with carbon, nickel, silver, etc., aluminum-cadmium alloy, etc. can be used.

The positive electrode current collector can have fine irregularities on its surface to strengthen the bonding force with the positive electrode active material, and can be in various forms such as a film, sheet, foil, mesh, net, porous body, foam, or nonwoven fabric.

The positive electrode active material layer may include a positive electrode active material, a binder, and a conductive material.

The positive electrode active material may be at least one selected from the group consisting of elemental sulfur (S ₈ ), an organic sulfur compound Li ₂ S _n (n≧1), and a carbon-sulfur polymer ((C ₂ S _x ) _n : x=2.5 to 50, n≧2). Preferably, inorganic sulfur (S ₈ ) can be used.

The sulfur contained in the positive electrode active material does not have electrical conductivity by itself, so it is used in combination with a conductive material such as a carbon material. As a result, the sulfur is contained in the form of a sulfur-carbon composite, and preferably, the positive electrode active material is a sulfur-carbon composite.

The carbon contained in the sulfur-carbon composite provides a porous carbon material with a framework in which the sulfur is uniformly and stably fixed, and complements the low electrical conductivity of sulfur, allowing the electrochemical reaction to proceed smoothly.

The porous carbon material can generally be produced by carbonizing various carbon precursors. The porous carbon material contains non-uniform pores, the average diameter of the pores is in the range of 1 to 200 nm, and the porosity or void ratio is in the range of 10 to 90% of the total volume of the porous carbon material. If the average diameter of the pores is less than the range, the pore size is only at the molecular level and impregnation with sulfur is impossible, and conversely, if it exceeds the range, the mechanical strength of the porous carbon material is weakened, making it unsuitable for application to the electrode manufacturing process.

The shape of the porous carbon material may be spherical, rod-shaped, needle-shaped, plate-shaped, tubular, or bulk-shaped, and any shape commonly used in lithium-sulfur batteries may be used without restriction.

The porous carbon material may be any material that has a porous structure or a high specific surface area and is commonly used in the art. For example, the porous carbon material may be at least one selected from the group consisting of graphite, graphene, carbon black such as denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, carbon nanotubes (CNT) such as single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT), carbon fibers such as graphite nanofibers (GNF), carbon nanofibers (CNF), and activated carbon fibers (ACF), graphite such as natural graphite, artificial graphite, and expanded graphite, and activated carbon, but is not limited thereto.

The method for producing the sulfur-carbon composite is not particularly limited in the present invention, and any method commonly used in the industry can be used.

In addition to the positive electrode active material, the positive electrode may further include one or more additives selected from transition metal elements, Group IIIA elements, Group IVA elements, sulfur compounds of these elements, and alloys of these elements with sulfur.

The transition metal elements include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Os, Ir, Pt, Au, or Hg, etc., the IIIA group elements include Al, Ga, In, Ti, etc., and the IVA group elements can include Ge, Sn, Pb, etc.

The conductive material electrically connects the electrolyte and the positive electrode active material and serves as a path through which electrons move from the current collector to the positive electrode active material. Any conductive material can be used without restriction.

For example, the conductive material may be graphite such as natural graphite or artificial graphite; carbon black such as Super-P, denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; carbon derivatives such as carbon nanotubes or fullerene; conductive fibers such as carbon fibers or metal fibers; carbon fluoride; metal powders such as aluminum or nickel powder; or conductive polymers such as polyaniline, polythiophene, polyacetylene, or polypyrrole, either alone or in combination.

The binder maintains the positive electrode active material on the positive electrode current collector and organically connects the positive electrode active materials to further increase the binding strength between them. Any binder known in the industry can be used.

For example, the binder may be a fluororesin-based binder including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE); a rubber-based binder including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; a cellulose-based binder including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; a polyalcohol-based binder including polyvinyl alcohol (PVA); or a polyacrylic acid (polyacrylic One or a mixture or copolymer of two or more selected from the group consisting of polyacrylic binders including polyacid, PAA; polyolefin binders including polyethylene and polypropylene; polyimide binders; polyester binders; and silane binders can be used.

The method for producing the positive electrode is not particularly limited in the present invention, and a method commonly used in the industry can be used. As an example, the positive electrode is produced by preparing a positive electrode slurry composition and then applying the composition to at least one surface of the positive electrode current collector.

The positive electrode slurry composition contains the positive electrode active material, conductive material, and binder described above, and may further contain other solvents.

The solvent used is one that can uniformly disperse the positive electrode active material, conductive material, and binder. As such a solvent, water is the most preferable aqueous solvent, and in this case, the water may be distilled water or deionized water. However, the solvent is not necessarily limited to this, and if necessary, a lower alcohol that can be easily mixed with water can be used. Examples of the lower alcohol include methanol, ethanol, propanol, isopropanol, butanol, etc., and these can be preferably mixed with water.

The sulfur loading in the positive electrode is 1 to 10 mAh/cm ² , preferably 1 to 6 mAh/cm ² .

The negative electrode may include a negative electrode current collector and a negative electrode active material layer applied to one or both sides of the negative electrode current collector. Alternatively, the negative electrode may be a lithium metal plate.

The negative electrode current collector is for supporting the negative electrode active material layer, and is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and can be selected from the group consisting of copper, aluminum, stainless steel, zinc, titanium, silver, palladium, nickel, iron, chromium, alloys thereof, and combinations thereof. The stainless steel can be surface-treated with carbon, nickel, titanium, or silver, and the alloy can be an aluminum-cadmium alloy, or it can be sintered carbon, a non-conductive polymer surface-treated with a conductive material, or a conductive polymer. Generally, a copper sheet is used as the negative electrode current collector.

The material may take a variety of forms, including films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics, with or without fine irregularities on the surface.

The negative electrode active material layer may contain a conductive material, a binder, etc. in addition to the negative electrode active material. In this case, the conductive material and the binder are as described above.

The negative electrode active material may include a material capable of reversibly intercalating or deintercalating lithium (Li ⁺ ), a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions, lithium metal, or a lithium alloy.

The material capable of reversibly inserting or deintercalating the lithium ion (Li ⁺ ) is, for example, crystalline carbon, amorphous carbon, or a mixture thereof. The material capable of reversibly forming a lithium-containing compound by reacting with the lithium ion (Li ⁺ ) is, for example, tin oxide, titanium nitride, or silicon. The lithium alloy is, for example, an alloy of lithium (Li) and a metal selected from the group consisting of sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn).

Preferably, the negative electrode active material can be lithium metal, specifically in the form of a lithium metal thin film or lithium metal powder.

The method for forming the negative electrode active material is not particularly limited, and any method for forming a layer or film commonly used in the industry can be used. For example, methods such as compression bonding, coating, and vapor deposition can be used. In addition, the negative electrode of the present invention also includes a case where a thin metallic lithium film is formed on a metal plate by initial charging after a battery is assembled without a thin lithium film on the current collector.

The electrolyte is used as a medium to induce an electrochemical oxidation or reduction reaction at the positive and negative electrodes, as described above.

The electrolyte is injected at an appropriate stage in the lithium-sulfur battery manufacturing process depending on the manufacturing process and required properties of the final product. That is, it is applied before or at the final stage of assembly of the lithium-sulfur battery.

A conventional separation membrane can be interposed between the positive and negative electrodes. The separation membrane is a physical separation membrane that has the function of physically separating the electrodes, and can be used without any particular restrictions as long as it is a membrane that is used as a conventional separation membrane. In particular, it is preferable for the membrane to have low resistance to the ion movement of the electrolyte and excellent electrolyte moisture retention.

The separator separates or insulates the positive electrode and the negative electrode from each other and allows lithium ions to be transported between the positive electrode and the negative electrode, and may be made of a porous non-conductive or insulating material. Any separator that is typically used as a separator in a lithium-sulfur battery may be used without any particular limitations. The separator may be an independent member such as a film, or may be a coating layer added to the positive electrode and/or the negative electrode.

The separator may be made of a porous substrate, which may be any porous substrate typically used in lithium-sulfur batteries. A porous polymer film may be used alone or in combination. For example, a nonwoven fabric or polyolefin-based porous membrane made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used, but is not limited thereto.

The material of the porous substrate is not particularly limited in the present invention, and any porous substrate typically used in lithium-sulfur batteries can be used. For example, the porous substrate may be a polyolefin such as polyethylene or polypropylene, a polyester such as polyethylene terephthalate or polybutylene terephthalate, a polyamide, polyacetal, polycarbonate, or polyimide. Polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalate, polytetrafluoroethylene, polyvinylidene fluoride It may include one or more materials selected from the group consisting of polyvinyl fluoride, polyacrylonitrile, cellulose, nylon, poly(p-phenylene benzobisoxazole) and polyarylate.

The thickness of the porous substrate is not particularly limited, but is 1 to 100 μm, preferably 5 to 50 μm. The thickness range of the porous substrate is not limited to the above range, but if the thickness is less than the above lower limit, the mechanical properties may be deteriorated and the separator may be easily damaged during use of the battery.

The average diameter and porosity of the pores present in the porous substrate are also not particularly limited, but are 0.1 to 50 μm and 10 to 95%, respectively.

In addition to the common winding process, the lithium-sulfur battery according to the present invention can also be manufactured through lamination, stacking and folding processes of the separator and electrodes.

The shape of the lithium-sulfur battery is not particularly limited, and it can be in a variety of shapes, including cylindrical, stacked, and coin shapes.

The following are preferred examples to aid in understanding the present invention. However, the following examples are provided merely to facilitate understanding of the present invention, and the present invention is not limited thereto.

Example: Preparation of lithium-sulfur battery Preparation of electrolyte for lithium-sulfur battery: Preparation Examples 1 to 24
[Production Example 1]
An organic solvent, 1,3-dioxolane and 1,2-dimethoxyethane, were mixed in a volume ratio (v/v) of 1:1, and 0.5 wt % of 2-methyl-1,3-dioxolane was added as an additive. 1M of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1 wt % of _LiNO3 were dissolved in the mixture to prepare an electrolyte for a lithium-sulfur battery.

[Production Examples 2 to 7]
The electrolyte for the lithium-sulfur battery was prepared in the same manner as in Preparation Example 1, except that the weight ratio of the additive 2-methyl-1,3-dioxolane was changed as shown in Table 1 below.

[Production Examples 8 to 14]
An electrolyte solution for a lithium-sulfur battery was prepared in the same manner as in Preparation Example 1, except that 4-methyl-1,3-dioxolane was used as an additive in a weight ratio as shown in Table 1 below.

[Production Examples 15 to 21]
An electrolyte solution for a lithium-sulfur battery was prepared in the same manner as in Preparation Example 1, except that 2-ethyl-2-methyl-1,3-dioxolane was used as an additive in a weight ratio as shown in Table 1 below.

[Production Example 22]
An electrolyte for a lithium-sulfur battery was prepared in the same manner as in Preparation Example 1, except that no additive was used.

[Production Examples 23 and 24]
An electrolyte for a lithium-sulfur battery was prepared in the same manner as in Preparation Example 1, except that 1,3-dioxolane was further added as an additive in the weight ratio shown in Table 1 below.

Fabrication of Lithium-Sulfur Batteries: Examples 1 to 21 and Comparative Examples 1 to 3
[Example 1]
A positive electrode active material slurry was prepared by mixing a positive electrode active material, a sulfur-carbon composite, a conductive material, and a binder in a ratio of 87.5:5:7.5 with water as a solvent. The sulfur-carbon composite was prepared by mixing sulfur and carbon nanotubes (CNTs) in a weight ratio of 75:25. In addition, a positive electrode slurry composition was prepared by mixing denka black as a conductive material and styrene-butadiene rubber/carboxymethyl cellulose (SBR:CMC=70:30, weight ratio) as a binder.

The positive electrode active material slurry was applied to one side of an aluminum current collector, dried at 100° C., and rolled to prepare a positive electrode having a porosity of 68% and a loading capacity of 5.6 mAh/cm ² .

A 45 μm thick lithium metal was used as the negative electrode.

The manufactured positive and negative electrodes were placed facing each other, and a polyethylene separator having a thickness of 16 μm and a porosity of 45% was interposed between the positive and negative electrodes to manufacture an electrode assembly. The electrode assembly was then placed inside a case, and the lithium-sulfur battery electrolyte of Manufacturing Example 1 was injected into the case to manufacture a lithium-sulfur battery.

[Examples 2 to 21]
A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the electrolyte solutions of Preparation Examples 2 to 21 were used as the lithium-sulfur battery electrolyte solutions.

[Comparative Examples 1 to 3]
A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that the electrolyte solutions of Preparation Examples 22 to 24 were used as the lithium-sulfur battery electrolyte solutions.

Experimental Example 1: Evaluation of Battery Life Characteristics The life characteristics of the lithium-sulfur batteries prepared according to Examples 1 to 21 and Comparative Examples 1 to 3 were evaluated by repeating charge and discharge cycles. The evaluation results are shown in Table 3 below.

Specifically, the lithium-sulfur battery was discharged twice at 0.1C to 1.8V and charged twice at 0.1C to 2.5V in CC mode at a battery operating temperature of 25°C, then charged and discharged once at 0.2C, and charged and discharged at 0.3C/0.5C for up to 200 cycles to evaluate the battery life characteristics.

In the battery life characteristic evaluation, the retention rate is defined as the ratio (%) of the discharge capacity at that cycle to the discharge capacity at the start of the 0.3C charge/0.5C discharge cycle, and the number of cycles at which the retention rate (%) reaches 80% to evaluate the battery life is shown in Table 3 below.

From the results in Table 3, it was confirmed that the lithium-sulfur batteries of Examples 1 to 7, which contain the dioxolane derivative 2-methyl-1,3-dioxolane as an electrolyte additive, maintain a high capacity retention rate even after repeated cycles and have excellent battery life characteristics, compared to Comparative Example 1, which contains no electrolyte additive, or Comparative Examples 2 and 3, which contain 1,3-dioxolane as an electrolyte additive.

Specifically, it was found that in Examples 1 to 7, which contain the dioxolane derivative 2-methyl-1,3-dioxolane as an electrolyte additive, the retention rate reaches 80% after at least 61 cycles. However, in the case of Comparative Examples 1 to 3, it was confirmed that the retention rate reaches 80% before 47 cycles, and the capacity retention rate due to charging and discharging is significantly reduced.

In particular, in the case of Examples 1 to 5, which contain the electrolyte additive "2-methyl-1,3-dioxolane" at 0.1 to 5% by weight relative to the total weight of the electrolyte, it was confirmed that the capacity retention rate was 80% or more even after more than 100 charge/discharge cycles, and that the battery had excellent life characteristics.

In addition, it was confirmed that in Examples 8 to 12 and Examples 15 to 19, in which "4-methyl-1,3-dioxolane" and "2-ethyl-2-methyl-1,3-dioxolane" were used as electrolyte additives at 0.1 to 5 wt % of the total weight of the electrolyte, respectively, they had higher capacity retention and excellent life characteristics compared to the cases in which the additive was added at more than 5 wt %.

All mere variations or modifications of the present invention are within the scope of the present invention, and the specific scope of protection of the present invention will be defined by the appended claims.

Claims (7)

An electrolyte for a lithium-sulfur battery comprising a lithium salt, an organic solvent and an additive,
The additive includes a compound represented by the following formula 1:
The electrolyte for lithium-sulfur batteries includes a compound represented by Chemical Formula 1 in an amount of 0.1 to 4.2 wt % based on the total weight of the electrolyte .
[Chemical Formula 1]
In the above Chemical Formula 1,
R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen; deuterium; a substituted or unsubstituted C1 to C60 alkyl group; a substituted or unsubstituted C6 to C60 aryl group; a substituted or unsubstituted C1 to C60 alkoxy group; and a substituted or unsubstituted C6 to C60 aryloxy group, wherein at least one of R1 to R6 is not H. The electrolyte for a lithium-sulfur battery according to claim 1, wherein R1 to R6 are the same or different and each independently selected from the group consisting of hydrogen; deuterium; a substituted or unsubstituted C1 to C20 alkyl group; a substituted or unsubstituted C6 to C20 aryl group; a substituted or unsubstituted C1 to C20 alkoxy group; and a substituted or unsubstituted C6 to C20 aryloxy group, and at least one of R1 to R6 is not H. The electrolyte for a lithium-sulfur battery according to claim 1, wherein R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen; deuterium; and substituted or unsubstituted C1 to C10 alkyl groups, and at least one of R1 to R6 is not H. The electrolyte for a lithium-sulfur battery according to claim 1, wherein R1 to R6 are the same or different and are each independently selected from the group consisting of hydrogen; deuterium; methyl; ethyl; propyl; n-propyl; isopropyl; butyl; n-butyl; isobutyl; tert-butyl; sec-butyl; 1-methyl-butyl; 1-ethyl-butyl; pentyl; n-pentyl; isopentyl; neopentyl; tert-pentyl; hexyl; n-hexyl; 1-methylpentyl; 2-methylpentyl; 4-methyl-2-pentyl; 3,3-dimethylbutyl; and 2-ethylbutyl; and at least one of R1 to R6 is not H. The electrolyte for lithium-sulfur batteries according to claim 1, wherein the compound represented by the chemical formula 1 is selected from the group consisting of 2-methyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 2-ethyl-2-methyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2,2,4-trimethyl-1,3-dioxolane, and combinations thereof. 2. The electrolyte for a lithium-sulfur battery according to claim 1, wherein the compound represented by Formula 1 is 2-methyl-1,3-dioxolane. Positive electrode;
Negative electrode;
A lithium-sulfur battery comprising: a separator interposed between the positive electrode and the negative electrode; and the electrolyte solution according to any one of claims 1 to 6 .